This application claims priority from JP 2003-317241 filed Sep. 9, 2003; JP 2003-317242 filed Sep. 9, 2003, and JP 2003-142495 filed May 20, 2003, the disclosures of which are incorporated in their entireties herein.
1. Field of Invention
This invention relates to a three-phase motor having a stator formed by inserting winding coils of three phases into slots provided on the inner circumferential surface of a stator core.
2. Description of Related Art
A stator, used for a three-phase motor, is formed by sequentially inserting winding coils of U-phase, V-phase and W-phase into many slots formed on the inner circumferential surface of the stator core.
A distributed winding type stator is known in which plural unipolar coils, formed by winding electric wires in plural turns and connected via a connecting wire, are used as the winding coil of each phase, and in which the unipolar coils of the winding coil of each phase are inserted in a distributed manner in many slots.
In the above-described distributed winding type stator, each unipolar coil of the winding coil of V-phase is offset with respect to each unipolar coil of the winding coil of U-phase and each unipolar coil of the winding coil of W-phase is offset with respect to each unipolar coil of the winding coil of V-phase in a circumferential direction by a predetermined number of slots, and each of these coils is thus inserted in each slot on the stator core. The remaining part of each unipolar coil of the winding coil of each phase that is not inserted in each slot protrudes from an end part in the axial direction of the stator core and forms a coil end part of each phase.
In a stator 92, as shown in FIG. 12, unipolar coils 931, 941, 951 of winding coils 93, 94, 95 of U-phase, V-phase and W-phase have substantially the same circumferential length.
Meanwhile, at coil end parts 932, 942, 952 of the phases, the coil end part 942 of V-phase is superposed on the inner circumferential side of the coil end part 932 of U-phase, and the coil end part 952 of W-phase is superposed on the inner circumferential side of the coil end part 942 of V-phase, as shown in FIG. 13. Therefore, to insert the winding coil 94 of V-phase into a stator core 921, the coil end part 932 of U-phase must be deformed and shifted toward the outer circumferential side of the stator core 921. Moreover, to insert the winding coil 95 of W-phase into the stator core 921, the coil end part 942 of V-phase must be deformed and shifted toward the outer circumferential side of the stator core 921.
Therefore, the coil end parts 932, 942, 952 of the above-described phases have the following shapes. That is, the coil end part 942 of V-phase protrudes from an end (side of the ring like stator) part 922 in the axial direction of the stator core 921 to a greater degree than the coil end part 932 of U-phase, and the coil end part 952 of W-phase protrudes from the end part 922 in the axial direction of the stator core 921 to a greater degree than the coil end part 942 of V-phase. This makes it difficult to reduce the overall dimensions of the coil end parts 932, 942, 952 of the three phases.
In a stator used for a single-phase motor, as described in JP-UM-A-5-78177, the circumferential length of a winding arranged on the inner circumferential side of a stator core is made shorter than the circumferential length of a winding arranged on the outer circumferential side and a sag at the coil end part is thus reduced to decrease the size of the coil end part.
However, in the three-phase motor, it is important to deform and shift the coil end parts 932, 942 of U-phase and V-phase toward the outer circumferential side of the stator core 921 by an optimum quantity. To this end, it is necessary to optimize the ratio of the lengths of the electric wires forming the coil end parts 932, 942, 952 of U-phase, V-phase and W-phase. Therefore, the technique of JP-UM-A-5-78177 cannot be directly applied to the three-phase motor.